When your car goes clunk over a bump in the night

  • Article by: PAUL BRAND
  • May 18, 2012 - 5:43 PM
Q I purchased a 2008 Buick Lucerne new, and it now has 68,000 miles. For the past 10,000 miles or so, a rattle or clunk noise has been coming from the front when it's driven over any kind of bump. It sounds like something is loose in the front end.

I am a bit anal about noises and squeaks, so it is really annoying. Upon inspection, the dealer found that the strut plates are worn, causing the problem. The struts are fine, but they want to replace the plates and struts for about $1,200. An independent shop said they could replace the plates only for $500. How can I be assured that this is the problem before making the investment of changing the plates? Is there any reason to replace the struts at the same time if they are just fine now?

A The McPherson strut mounting plates at the top of the strut are fitted with bearings to allow the strut to rotate as you steer the vehicle. Wear in the strut bearings could certainly cause the type of noise you describe. But so could worn stabilizer bar or link bushings, loose brake pads or worn lower ball joints. Get a second opinion by having a tire or independent shop inspect the front suspension components.

If the strut plates are worn, they can be replaced individually. Back in the day, at 70,000 miles I would have suggested the struts be replaced at the same time. But today's shocks and struts are far better quality and last much longer, so unless there's evidence of a leak or a problem with the ride, I wouldn't replace the struts themselves.

Q I have a 2009 Prius with about 22,000 miles. In local driving, when I slow to 15 to 20 miles per hour and then apply the brakes lightly with the wheel turned an eighth-turn to the right, I hear a ticking or ratcheting noise coming from the front. I have twice taken it to the dealer, but the noise is absent after I get there. The service tech suspected a CV joint problem but found no evidence of malfunction. I think the noise originates higher than that, possibly toward the bulkhead behind the engine, but he said he had no other ideas without hearing the noise.

A I would not suspect a CV joint to make noise under light braking. I would first focus on the front brakes. If one of the brake pads is loose, it may click as it moves back and forth within the caliper. Check for play in the front hub/wheel bearing assemblies, and don't overlook possibilities such as an inboard wheel weight hitting the caliper, or, if the vehicle is equipped with wheel covers, a loose spring clip rattling against the wheel.

Q I have a 2000 Mercury Mountaineer that binds up on corners at slow speeds. It does not have rear clutch packs, and the CV joints are good. The only thing I can think of is that the transfer case is not free-wheeling when I turn. I'm going to pull the front drive shaft and try it, but please save me. Do you think it is the chain or clutch in transfer case?

A Before you do anything else, swap the front tires onto the rear and see if the binding still occurs. One tire more than 1 or 2 percent larger or smaller than the others may be the problem.

According to my Alldata automotive database, your vehicle could feature an all-wheel drive system or a selectable four-wheel drive system. So it could be fitted with a limited-slip rear differential. If so, make sure it is filled with the proper 75w-140 limited-slip lubricant.

Are noises associated with the binding? If so, and the noise is there no matter what gear the transmission is in, the problem may be the input gear or front output shaft gear in the transfer case.

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